How do I resize an existing Wubi installation?

Question

I have Windows 7 as my default OS and 500 GB Hard Disk.

Following is the partition table of my Hard Disk:

I have installed Ubuntu with "install inside windows" option.

• sda1 is the System Reserved space for Windows 7
• sda2 is the Windows partition (C: Drive)
• sda3 is the Partition inside which I have installed Ubuntu, i.e., it is installed in a folder called Ubuntu. I also have some other files in the 200GB partiton
• sda4 is the common drive where I store all the stuff like Music, Movies, Projects etc.

Now the problem is I have allocated only 25GB as the default installation size in WUBI installer. But I want to increase the size from 25GB to 75 GB or more without losing any files neither in Windows nor Ubuntu.

How do I do that?